S78 



The Need for Lime : How to Meet It. 



[Jan., 



the hood. Hoods are apt to prove dangerous to the men 

 charging the kiln by reason of the gases which collect in them, 

 and unless the situation of the kiln is ill chosen with reference 

 to the prevailing winds, hoods are best avoided. 



The taller the kiln the better it is for draught, regenerative, 

 and pre-heating efficiency, but there are two important limita- 

 tions — (1) great height without proportionate increase in 

 diameter so increases the radiating surface per unit capacity 

 of kiln that the heat losses begin to increase, and (2) height 

 must be proportioned to the resistance which the particular 

 stone offers to crushing both before and after it is burnt. This 

 consideraion, if neglected, may lead to so much breaking up 

 and packing of the charge that the draught is destroyed. 



It is possible to burn a fairly crushable stone, such as oolite 

 or chalk, in a tall kiln if either of the following devices are 

 resorted to : — (a) The kiln lining may be made elliptical in plan 

 in such a way that the major axis shrinks and the minor expands 

 until they have changed places as it descends the kiln; (/>) A 

 pair of obstructing rounded shoulders may be formed in the. 

 lining so that the charge descends by a slightly zig-zag motion. 

 By the use of either (a) or (h) much of the weight of the charge 

 is taken upon the kiln w^alls rather than upon the lime in, or 

 below, the reaction zone, and crushing is thereby minimised. 



Single and therefore unsymmetrical draw eyes are objection- 

 able, particularly in short kilns, because they cause uneven 

 draught and descent of the charge. An arched circular passage 

 entered from the front and built in the thickness of the wall 

 a.t the base of the kiln has been successfully employed to enal:)le 

 four draw^ eyes to be conveniently vrorked in each of a battery 

 of kilns with access to the front only. The size of the stone 

 composing the charge may increase with the size of kiln. In 

 a big kiln it is possible to burn thoroughly large blocks of stone 

 which would leave a large residue of core if calcined in a small 

 kiln. The more nearly the blocks are cubical (not flakes) and 

 the more uniform they are in size the better will be the draught; 

 a lot of small stuff in the charge fills the voids and makes a 

 good draught impossible. The fuels which can be used in 

 shaft kilns are limited to anthracite (small anthracite or 

 " culm " is usually employed^ hard steam coal, and gas coke. 



Treatment of the Lime. — Now that lime is so comparatively 

 expensive a product it is no longer reasonable to distribute it 

 in lumps over the land and leave time and the weather to effect 

 an even distribution, which, it may be added to their discredit, 

 they never did accomplish. Something must always be done 



